1. Field of the Invention
This invention relates to speed transducers for a rotatable shaft and more particularly to a brushless tachometer which provides a DC voltage indicative of shaft speed and direction of rotation.
2. Description of the Prior Art
Brushless speed indicators are utilized for many drives wherein, due to specific conditions, no commutators or brushes may be considered for use, or where a speed indicator free from maintenance is required. Applicant is unaware of any prior art which teaches using a multi-pole printed circuit resolver to provide a signal which is processed to yield a bi-directional speed indication. Several prior art brushless tachometers are known which utilize rotatable inductors or rotatable permanent magnets. Most prior art tachometers are AC and provide no polarity change for the change in the direction of rotation.
U.S. Pat. No. 3,839,665 discloses a transducer which is coupled to a motor shaft to provide both position and velocity information.
U.S. Pat. No. 3,604,869 discloses a device which produces a direct voltage speed indication. The device of U.S. Pat. No. 3,604,869 utilizes a multi-phase AC voltage machine having a rotatable inductor.
U.S. Pat. No. 3,508,137 teaches a brushless DC tachometer which is constructed with a permanent magnet rotor which generates a flux field which cuts conductors of stator windings to induce voltages therein. This tachometer utilizes a plurality of photo transistors to improve the output linearity of the tachometer. U.S. Pat. No. 3,858,109 teaches a brushless tachometer having a multi-pole permanent magnet rotor and a two phase stator.
U.S. Pat. No. 3,848,157 teaches a brushless DC tachometer. This tachometer does not use a position sensing device for providing the information which is processed to yield the speed signal.